This invention is concerned with stratified charge internal combustion engines, wherein the charge mixture or elements are subjected to a high transfer motion, during the compression cycle, consisting essentially of induction swirl and squish action. This type of invention is commonly referred to in the art as a programmed combustion engine (PROCO) which has been developed by the assignee hereof, and is particularly depicted in U.S. Pat. Nos. 3,315,650; 3,439,656; and 3,696,798.
This type of stratified charge combustion process employs an essentially unthrottled charge of air which is taken into the engine at all times; fuel is injected directly into a localized portion of this charge of air in a main combustion chamber defined by the piston and cylinder, the fuel being varied with load and operating requirements of the engine. The pressure and fuel controls being such as to cause a slow dispersing of the fuel particles into the air in a manner permitting the control of the air-fuel ratio change so that the local mixture can be ignited at the proper time to assure more complete combustion within a predetermined crankshaft rotation and before the overall air-fuel ratio becomes too lean.
Post-ignition turbulence of the charge is assured by the combination of the induction swirl and squish action. Induction swirl is promoted principally by locating the induction port and valve offcenter and non-radial with respect to the axis of the cylinder, whereby a swirl motion is imparted to the air as it is sucked into the main cylinder. The swirl rate is proportional to the crankshaft speed and the only requirement is that it be repeatable from cycle to cycle and cylinder to cylinder.
Squish action is promoted by locating the main combustion chamber (as a cup) in the piston so that the uninterrupted top surface of the piston may be moved to critically close spacing (squish zone) with the head of the cylinder at top dead center, the space being limited to a dimension of 0.06-0.10 inches. The air or charge elements residing in this progressively decreasing squish zone, between the uninterrupted top surface of the piston and the cylinder head, are forced to move radially inwardly. The mass of air, converging towards the center of the upper most region of the cylinder, is forced to turn downward as it reaches the central region forming an air column which moves downwardly meeting the bottom of the cavity within the piston and spreading radially outwardly therefrom.
In the conventional PROCO combustion system two problems are of great concern: (a) the high transfer motion tends to extinguish the starting flame, and (b) even if the flame is not extinguished, there is an entrapment of unburned charge elements in the squish zone. With respect to the first problem, it must be emphasized that the use of the cavity or cup within the top of the piston is essential to better engine efficiency, because at low loads, fuel can be injected principally into the cup close to top dead center and combustion can be confined principally to the cup itself. At high loads, fuel can be injected earlier into the cylinder which would include the squish zone in addition to the cup or cavity thereby giving considerably increased power. Accordingly, it is important that the concept of high charge transfer motion be retained to maintain the benefits of programmed combustion, but without the extinguishment of the combustion flame.
Turning to the second problem; typically, a PROCO combustion system is ignited by the use of a single spark plug. The initiation of combustion is timed such that fuel injection is introduced considerably early but the flame does not reach the squish zone until top dead center is substantially achieved, thereby resulting in high hydrocarbons. Even when two spark plugs are used, arranged symmetrically on either side of a centrally located fuel injector, the problem of uncombusted hydrocarbons remains. With two spark plugs, more exhaust gas recirculation may be incorporated permitting somewhat later injection of the fuel, but initiation of the combustion must still be maintained at a moment close to top dead center which results in the trapping of hydrocarbons in the squish zone. What is needed is a system whereby fuel injected into the squish zone, as well as the cup or cavity, can be continuously moved by charge transfer motion into the cup where the initiation of combustion can take place prior to the attainment of top dead center and the combusted gases resulting from combustion in the cup can be moved to displace the unburned hydrocarbons in the squish zone.